Firefox has no problem with %00 links

Yep, Firefox works fine. Vivaldi 1.0.219.50 also crashes the tab on hover.

Vivaldi is just a fork of Chrome with a lot of GUI stripped away, then reimplemented in JS.

Wow... I thought my newly built Hackintosh was unstable until I realized it was the link and checked the source.

Why is this happening?

%30 encodes for 0, so %%30%30 should decode to %00, which is the urlencoding for a null char. My guess is that this either crashes the engine as it tries to open the URL with a null byte in it, or the GUI as it tries to display the tooltip.

A bit of reading on the null byte from a web development perspective: http://projects.webappsec.org/w/page/13246949/Null%20Byte%20...

Interestingly enough, trying to open this link from Thunderbird 38.2.0's feed reader does nothing and opening it in Opera 32.0.1948.25 crashes the browser. Hovering over the link in Opera crashes the tab, probably due to some prefetching...

Opera 15+ operates identically to Chrome because it is just a fork with minimal amounts of changes.

Tried to open from Chrome Developer Tools, it crashed it on hover too.

You might want to file a bug report, if there isn't one already. I have filed bug reports for Opera and Vivaldi.